The present invention relates generally to weight sensors and more particularly to a magnetostrictive weight sensor for a vehicle seat.
Current vehicles include active restraints, such as airbags. It is desirable to determine whether an occupant is present in a vehicle seat and to determine the weight of the occupant in the vehicle seat. The active restraint may be disabled if the seat is not occupied, or is the occupant is a child. It may also be desirable to vary the strength with which the active restraint is deployed based upon the weight of the occupant.
U.S. Pat. No. 5,739,757, the Assignee of which is the Assignee of this invention, describes a weight sensor using a magnetostrictive sensor. The magnetostrictive sensor is positioned adjacent a ferromagnetic element, such as a wire in the seat. The magnetostrictive sensor includes a ferrite core having an excitation coil which when driven by a function generator forms an electromagnet. The sensor further includes a detection coil also coiled about the ferrite core. An electromotive force voltage is induced in the detection coil by the electromagnet. When a weight, such as a passenger, is placed upon the seating surface, the weight is transmitted to the ferromagnetic element, thereby inducing strain in the ferromagnetic element. The strain in the ferromagnetic element alters the magnetic field in the electromotive force voltage generated by the detection coil. By analyzing the signal generated by the detection coil, the weight upon the seating surface can be determined.